Hello Alex
I have repaired many such CCS 800s in my long years as a Märklin "surgeon"!
This one is yet another occurrence of Dr Frankenstein's intervention

and he did not do a good job IMHO!
As you and others noted correctly yours is a newer chassis with an older body rigged on to it.
So that is bad news and good news!
The bad news is that it will probably never be "close to original" as you wish...
You can find the replacement end chassis , but there is no such thing for the middle part: dead end!
The good news is that the part that is broken (the center chassis) for the newer versions is still available from Ritter.
So there is hope
Lastly I even adapted one to a true 1947 older Krok, for which I had to do some minor machining/adaptation to the end chassis.
(BTW, your nose pieces are also missing the contact plates for the bulbs)
So overall I think that it is actually a good situation because the newer version run **much** better that the old ones.
I just think that it will take some very careful thinking and accurate machining to properly attach the body nose pieces to their chassis.
The original version is totally different from the newer versions.
I don't even think there is material on the older bodies to drill/machine the two threaded holes that would fit in the newer chassis ...and vice-versa!!
If needed, I can look into my various exemplars on what the options are.
You may probably have to fabricate studs that would then have to be epoxy-ed in the body.
If you decide to go that way and that you have the proper milling/drilling machine I could provide you with a diagram with accurate measurements.
It will be quoted in mm though, if you need inches, you'll have get the calculator out!
FYI:
In any case, adapting the RITTER reproduction end chassis for the original version is not for the faint of heart!
Because of the metal shrinkage (as it cools down after injection) the holes for the wheels and gears are**never** at the right spot and even worse, they are not even perpendicular to the chassis axis of symmetry!
So the only way to do that job correctly is to fill the repro chassis holes back with bronze rods, then re-machine the chassis properly on a milling machine with two axis precision positioning.
Interesting surgery though...
Niuk, niuk, niuk!
Cheers